The present invention relates to a pressure sensitive sensor, an object-detecting device, attachment structure thereof and an opening and closing device. More particularly, the invention relates to a technique for improvement to reliably operate a sensor and a pressure sensitive sensor attachment structure and an opening and closing device which are suitably used for a power window device of a car which requires an object pinching preventing function.
Conventionally, there have been disclosed many examples in which a pressure sensitive sensor of such a type as to close a contact point by pressing or a piezoelectric sensor utilizing a piezoelectric element is used for a pressure sensitive sensor to be used for preventing an object from being pinched. When the piezoelectric sensor is deformed by the pressing of an object, a voltage pulse is output from the piezoelectric sensor and the presence of pinching of the object is detected based on the presence of the voltage pulse. In the case in which these pressure sensitive sensors are applied to prevent pinching in the power window device of a car, a pressure sensitive switch or a piezoelectric sensor is provided along the window frame of a door and is deformed by an object when the object is pinched between the window frame and a windowpane, for example. If the pressure sensitive switch is closed or a predetermined voltage pulse is output from the piezoelectric sensor when the windowpane is to be closed, it is assumed that the object is pinched and the direction of rotation of an electric motor is reversed to eliminate the pinching.
There has been proposed the pinching detecting device for the power window device of this type comprising a pressure sensitive sensor 210 having conductive contact wires 202, 203, 204 and 205 opposed on the inner circumference of a long string-shaped elastic cylinder 201 which is buried in elastic support means provided along the edge of a window frame as shown in FIGS. 22A and 22B (for example, see Japanese Patent Document JP-A-2001-153734).
The pressure sensitive sensor 210 serves to output a predetermined detection signal when conductive contact wires to be opposed to each other in the elastic cylinder 201 come in contact with each other as shown in FIG. 23B when the elastic cylinder 201 is crushed in a constant amount or more by pinching an object.
In the pinching detecting device using the pressure sensitive sensor 210, however, when the pressure sensitive sensor 210 is bent as shown in FIG. 23A corresponding to the corner section of a window frame in order to be provided along the corner section of the window frame in the front seat of a vehicle, for example, there is a possibility that the elastic cylinder 201 might be crushed in a bending position and the contact wires might thereby come in contact with each other, resulting in erroneous detection as shown in FIG. 23B. For this reason, the pressure sensitive sensor 210 has conventionally been provided independently for each of almost rectilinear sides constituting the window frame such that one pressure sensitive sensor 210 is not provided across the corner section of the window frame.
In such a pressure sensitive sensor attachment structure, however, there is a problem in that the number of the pressure sensitive sensors 210 to be used is increased and a great deal of time and labor is required for a processing of connecting a lead wire from each pressure sensitive sensor 210.
In the pressure sensitive sensor attachment structure, moreover, a pressure sensitive sensor is not present in the corner section itself of a window frame. For this reason, there is a possibility that the local pinching of an object in the corner section of the window frame might not be detected.
In the pressure sensitive sensor 210, furthermore, even if the section of the pressure sensitive sensor 210 is crushed due to the pinching of an object, the contact of the contact wires is not generated until the section is crushed in a constant amount or more. Consequently, the pinching is detected with a delay. As a result, there is a problem in that an operation for closing a windowpane is stopped with a delay.
In the case in which an inclined side is provided on the window frame as in an opening and closing door in the front seat of a vehicle, force acting in such a direction as to deform the section of the pressure sensitive sensor 210 is changed into a component of force which is smaller than force for lifting a windowpane pinching an object when the object is pinched in the pressure sensitive sensor 210 provided on the inclined side. As a result, the elastic cylinder 201 is not sufficiently deformed elastically. Finally, there is a possibility that the pinching of the object might not be detected quickly.
On the other hand, in the piezoelectric sensor, moreover, there is a problem in that the piezoelectric sensor is fixed to the window frame and is thus deformed with difficulty even if the object presses the piezoelectric sensor, and a voltage pulse having a sufficient magnitude for detection is not generated from the piezoelectric sensor when pinching is to be detected. For this reason, the voltage pulse having a sufficient magnitude is not output from the piezoelectric sensor. Therefore, a windowpane continuously carries out a closing operation until the voltage pulse has a detection threshold or more for the pinching. Consequently, there is a possibility that a load applied to the object might be increased to damage the object before the pinching is eliminated.
Therefore, there has been disclosed in Japanese Patent Document JP-A-2001-324393 a technique in which a pressure sensitive sensor utilizing a novel piezoelectric element formed like a flexible wire and serving to generate an output signal corresponding to the acceleration component of deformation is used to enhance a detection sensitivity, thereby producing great pinching prevention effects (see FIGS. 1, 2 and 4).
The pressure sensitive sensor for generating an output signal corresponding to an acceleration component is attached to a window frame 1 with a structure shown in FIG. 14. More specifically, a pressure sensitive sensor 4 comprises a flexible piezoelectric sensor 2 and support means 3, and the support means 3 has the piezoelectric sensor 2 provided in the vicinity of a lowermost portion and is formed of an elastic member such as rubber having a flexibility or a foamed resin member. Moreover, the thickness of the support means 3 provided around the piezoelectric sensor 2 is reduced such that the piezoelectric sensor 2 can easily be deformed. The support means 3 has a deformation increasing section including a hollow section 4 and a side wall section 5 which serves to increase the deformation of the piezoelectric sensor 2.
In the attachment structure, the deformation of the piezoelectric sensor 2 is mainly increased by the deformation of the deformation increasing section so that a high detection sensitivity can be realized. As a result of the vigorous investigations of the inventors, however, it could be known that a detection capability can be enhanced still more at a low cost by varying the signal processing of the piezoelectric sensor 2 or changing the shape of the support means 3.